1. Field of the Invention
The present invention relates to circuit module heating technology, and more particularly to a heating element and circuit module stack structure that automatically turns on an electrical heating element to heat the chip unit of the circuit module when the temperature of the chip unit drops below 0° C. under a cold weather environment, and automatically turns off the electrical heating element when the temperature reaches a predetermined normal operating temperature range.
2. Description of the Related Art
Following fast development of computer electronic technology, desk computers, notebook computers, and other related products with high power, high operation speed, large capacity and low profile characteristics have been continuously created. However, during operation of a computer, the CPU, graphic processor and other components of the computer will release waste heat. An electronic component having a relatively higher operation speed can generate a relatively larger amount of waste heat. It is important to provide a computer with a heat dissipation structure, enabling the CPU or other electronic components to work within the normal operating temperature range.
Further, heat sinks are commonly used in computers and kept in close contact with chips (CPU, graphic processor, etc.) for quick dissipation of waste heat. An electric fan may be attached to a heat sink to enhance dissipation of heat. Using a chip unit at a circuit board under a normal room temperature environment simply needs to consider the problem of overheat due to a high operation speed. However, using a computer under a severe weather condition where the temperature and moisture changes in an extremely wide range, or in a desert, snow place or any other place where there is a large temperature difference between day and night or the weather is extremely cold, the computer may be unable to start up the CPU.
A computer system may be used in a severe weather environment. Therefore, a computer system can be configured to work under the temperature range of −40° C.˜++80° C. However, because the normal operating temperature range of computer electronic components (either active or passive components) is set in the range of 0° C.˜++75° C., the internal temperature of the computer must be kept within this normal operating temperature range if the computer is used in a cold outdoor environment under 0° C. For allowing a computer to be used in a severe cold weather environment, the computer may be wrapped or stuffed with heat insulating materials to protect internal electronic components against outside cold air. However, because it is the market trend to create computers having light, thin, short and small characteristics, wrapping or stuffing a computer with heat insulating materials cannot meet this computer design requirements. Further, because a computer has many connectors and buttons, the use of heat insulating materials cannot fully protect the computer internal components against outside cold air.
In order to eliminate the drawbacks of the use of heat insulating materials in a computer, an electrical heating device may be installed in a circuit board in a computer to be used under a severe weather environment. An electrical heating device for this purpose is known comprising a heating layer, a DC power source, and a current regulator. The heating layer is set in between insulating layers in the circuit board, comprising a heating circuit having a predetermined resistance and prepared from an electrically conductive material. The DC power source is adapted to provide direct current to the heating circuit of the heating layer. The current regulator is adapted to regulate the volume of the current at the heating circuit. When the heating circuit of the heating layer is electrically conducted, it generates heat that is then transferred by a metal circuit layer of the circuit board to the electronic components at the metal circuit layer to heat the electronic components to the normal operating temperature range. However, because the circuit board carries a large amount of electronic components that are densely installed in the circuit board, it is complicated to install the heating layer in the insulating layers and metal circuit layer of the circuit board, leading to increase in manufacturing cost.
Further, a circuit board manufacture may install a heating module in the circuit board. The heating module comprises a metal-oxide-semiconductor field-effect transistors (MOSFETs), a DC power source, a current sensor, and a dynamic resistance controller. The MOSFETs are mounted at the surface of the circuit board. The DC power source is adapted to provide a DC voltage to the MOSFETs. The dynamic resistance controller is adapted to regulate the on-state resistance of the MOSFETs subject to the intensity of the DC current detected by the current sensor, keeping the MOSFETs in the critical state between on and off state to continuously generate heat. The heat generated by the MOSFETs is dissipated to the surrounding area around the electronic components at the circuit board, keeping the electronic components in the normal operating temperature range. However, the installation of the MOSFETs complicates the spatial arrangement of the circuit board. In the circuit board, the electronic components at the circuit board that are disposed close to the MOSFETs receive better heating effects, however, the electronic components at the circuit board that are disposed far from the MOSFETs cannot receive optimal heating effects. Further, the use of the MOSFETs and the dynamic resistance controller greatly increases the cost of the heating module. An improvement in this regard is desired.